1. Field of the Invention
This invention relates to a fluorescent display device incorporating its driving IC therein, more particularly, relates to a structure of a filament end-supporting member of the fluorescent display device.
2. Background of the Invention
There has been conventionally proposed a fluorescent display device incorporating its driving IC therein (i.e., a driving IC-incorporated fluorescent display device), and having a retainer plate and a support of a filament end-supporting member as a shielding member to shield and protect the driving IC from electrons emitted from a filament (i.e., cathode).
FIGS. 4A and 4B are cross-sectional views of the conventional driving IC-incorporated fluorescent display device, and having the filament end-supporting member having the retainer plate and the support, as the shielding member.
FIG. 4A is a cross-sectional view of FIG. 4B taken along line X13-X13, and FIG. 4B is a cross-sectional view of FIG. 4A taken along line X12-X12.
The filament end-supporting member includes a retainer plate 21 and a support 22. The retainer plate 21 is provided with a rising portion 211 and a tabular portion 212, and the both ends of the retainer plate 21 are drawn from a joint portion X11 between an anode substrate 11 and a side plate (i.e., side member) 12 to outside of an enclosure. The support 22 includes a tabular portion 221, a rising portion 222, and a filament-attaching portion 223, and the tabular portion 221 of the support 22 is spot welded to the tabular portion 212 of the retainer plate 21. The end portion of a filament F is sandwiched between the filament-attaching portion 223 of the support 22 and a ribbon 23, and the ribbon 23 is fixed to the filament-attaching portion 223 by spot welding. The tabular portion 212 of the retainer plate 21 and the tabular portion 221 of the support 22 lie between the filament F and the driving IC 24 so as to function as shielding members of the driving IC 24. Furthermore, the reference numeral 25 indicates an anode electrode, which forms a fluorescent film.
The filament end-supporting member in FIG. 4 is formed of the retainer plate 21 and the support 22, and the support 22 includes the rising portion 222. For the reason, the distance between the filament F and the anode electrode 25 (height of the filament) becomes large. In other words, the height of the filament increases.
Therefore, in order to suppress the height of the filament F, there has been proposed a new filament end-supporting member in which the support 22 of the filament end-supporting member is omitted and the filament F is directly attached to the retainer plate 21. See for example, Japanese Unexamined Patent Publication No. 2011-243377.
FIGS. 5A and 5B are cross-sectional views of a driving IC-incorporated fluorescent display device, which employs the firmament end-supporting member having no support, as the shielding member.
FIG. 5A is a cross sectional view of FIG. 5B taken along line X23-X23, and FIG. 5B is a cross sectional view of FIG. 5A taken along line X22-X22.
The end portion of the filament F is sandwiched between a tabular member 262 of a retainer plate 26 also having a function as a support and the ribbon 23, and the ribbon 23 is fixed to the tabular portion 262 by spot welding. If the filament F is brought in contact with the tabular portion 262, the heat of the filament F is transferred to the tabular portion 262. As a so-called end cool region increases, the tabular portion 262 has a plurality of comb-like slits (i.e., opening portions) 262s at an area with which the filament F is in contact.
The filament end-supporting member in FIG. 5 does not provide for the support as shown in FIG. 3, and the height of the filament F can be decreased accordingly. Furthermore, reference numeral 261 represents a rising portion of the retainer plate 26.
A conventional filament end-supporting member in which a support is omitted provides advantages of decreasing a height of a filament. On the other hand, the conventional filament end-supporting member has disadvantages as mentioned below.
In FIG. 5, the retainer plate 26 is fixed between the anode substrate 11 and the side plate (side member) 12 at the area of X21 by the glass-based adhesive, and Alloy 42-6 thermal expansion coefficient of which is comparable to that of the adhesive is used, in order to prevent crack creation at the area of X21. Alloy 42-6 forms Cr oxide film by being subjected to heating treatment in hydrogen atmosphere in order to enhance adhesive strength to glass and air tightness. For the reasons, when the filament F is directly attached to the retainer plate 26 by welding, the welding strength can be lowered.
Also, as the slits 262s are formed just under the filament F, there is a risk that electrons which are emitted from the filament F may reach the driving IC 24 through the slits 262s. In this case, shielding effect might be compromised. Similarly, in the configuration in which the slits 262s are formed in the retainer plate 26, due to the three-dimensional conformation of the retainer plate 26 there is a risk of causing decrease in strength.